1. Field of the Invention
The present invention relates to a motion vector detecting apparatus for executing motion searches on the basis of variable block sizes so as to detect a motion vector, and more particularly to a motion vector detecting apparatus for detecting a motion vector which is used for predicting a motion compensation in a high efficiency coding of a digital motion picture signal.
2. Description of the Related Art
In the high efficiency coding system for coding the sequentially input motion picture signals by a less coding amount, there is a motion compensation prediction coding system as a coding system utilizing a correlation between the picture signals. In the motion compensation prediction coding, it is possible to widely reduce a coding amount by detecting a block having a highest correlation within a reference picture in the input picture, and coding a motion vector expressing the motion and a prediction error between the input picture and the reference picture.
It is possible to further reduce the prediction error by using variable block sizes as an area unit for executing the detection of the motion vector and the motion compensation, and it is possible to further reduce the coding amount. For example, in H.264 corresponding to an international standard of the picture coding, the coding is executed by constituting the area unit for executing the motion compensation by four kinds of block sizes comprising 8×8 pixels, 8×16 pixels, 16×8 pixels and 16×16 pixels as shown in FIGS. 1A, 1B, 1C and 1D, and selecting the block size having a higher coding efficiency among them. Further, in the case that the block size of 8×8 pixels is selected, it is possible to further separate each of the blocks into 4×4 pixels, 4×8 pixels and 8×4 pixels.
A simplest structure of the motion vector detecting apparatus for detecting the motion vector by setting variable block sizes as a unit is a system (hereinafter, refer to as a first system) of determining a motion vector which minimizes the prediction error in all the block sizes, and selecting the block size in which the prediction error is the minimum.
Further, in the following patent document 1, there is proposed a system (hereinafter, refer to as a second system) of reducing the block size to be selected in a process of the motion search, by comparing the prediction error per the block sizes in the middle of the motion search and passing over the large block size at a time when a predetermined condition is satisfied so as to execute the motion search.
[Patent document 1] Japanese Unexamined Patent Publication No. 2003-111082
In the first system mentioned above, since the motion search is executed with respect to all the block sizes, there is a problem that a calculation amount becomes huge, and a processing speed is lowered.
Further, in the second system mentioned above, since the block size to be selected is excluded in the middle of the motion searching process, a higher processing speed can be expected in comparison with the first system, however, since the motion searches of variable block sizes are executed in parallel until the partway stage, there is a problem that a lot of calculation amount is required.